A screw conveyor of this kind is described in U.S. Pat. No. 3,885,734 and in U.S. Pat. No. 3,934,792.
In a screw conveyor according to U.S. Pat. No. 3,885,734 the above mentioned baffle has the form of an annular disc arranged in a plane substantially perpendicular to the rotational axis.
In a screw conveyor according to U.S. Pat. No. 3,934,792, on the other hand, the baffle is arranged between two adjacent parts of the conveyor thread, extending substantially radially and axially with respect to said rotational axis.
Also WO 99/65610 shows a screw conveyor of the initially defined kind.
Traditionally, screw conveyors for decanter centrifuges have been manufactured out of metal, a strip of sheet metal having been formed into a screw thread and been welded along its radially inner screw-formed edge onto the central body. When desired a baffle of the kind defined above has been welded to the screw thread and possibly even to the central body.
In WO 99/65610 it is mentioned that the rotor and the screw conveyor may be formed of several parts, being releasably connected to each other and also that the screw conveyor may be manufactured in one piece of plastic. However, it is not mentioned more precisely any method for manufacturing of a screw conveyor. A general method for manufacturing of plastic details is injection moulding. However, this method appears not to be appropriate for any of the embodiments of the screw conveyor as shown in WO 99/65610. Thus, it does not appear to be possible to remove an injection-moulded screw conveyor from the mould by screwing it out thereof.
Also in U.S. Pat. No. 5,800,332 there is shown a decanter centrifuge, in which the rotor and the screw conveyor may be formed of several parts being releasably connected to each other.
An object of the present invention is to provide a construction for a screw conveyor, which construction makes possible a simple manufacture of the screw conveyor-even if it is to be made of plastic-ensures transportation of solid particles in the rotor past said baffle and gives stiffness and strength to the conveyor thread in an area where it intersects with the baffle.
Another object of the present invention is to provide a construction for a screw conveyor, which makes possible simple assembly of the screw conveyor.